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2 Documentation for Kdump - The kexec-based Crash Dumping Solution
11 Kdump uses kexec to quickly boot to a dump-capture kernel whenever a
14 the reboot and is accessible to the dump-capture kernel.
24 the dump-capture kernel. This ensures that ongoing Direct Memory Access
25 (DMA) from the system kernel does not corrupt the dump-capture kernel.
26 The kexec -p command loads the dump-capture kernel into this reserved
31 low 1M is reserved to avoid any later kernel or device driver writing
32 data into this area. Like this, the low 1M can be reused as system RAM
47 passed to the dump-capture kernel through the elfcorehdr= boot
51 With the dump-capture kernel, you can access the memory image through
52 /proc/vmcore. This exports the dump as an ELF-format file that you can
55 options, e.g with '-d 31' it will only write out kernel data. Further,
63 Install kexec-tools
64 -------------------
68 2) Download the kexec-tools user-space package from the following URL:
70 http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz
74 The latest kexec-tools git tree is available at:
76 - git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
77 - http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
80 http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git
82 More information about kexec-tools can be found at
87 tar xvpzf kexec-tools.tar.gz
89 4) Change to the kexec-tools directory, as follows::
91 cd kexec-tools-VERSION
106 Build the system and dump-capture kernels
107 -----------------------------------------
110 1) Build a separate custom dump-capture kernel for capturing the
113 2) Or use the system kernel binary itself as dump-capture kernel and there is
114 no need to build a separate dump-capture kernel. This is possible
125 dump-capture kernels for enabling kdump support.
128 ----------------------------
139 2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
159 Dump-capture kernel config options (Arch Independent)
160 -----------------------------------------------------
171 2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems"::
177 Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
178 --------------------------------------------------------------------
190 command line when loading the dump-capture kernel because one
212 kexec boot loader will load it in memory region reserved for dump-capture
217 start of memory region reserved for dump-capture kernel.
224 Dump-capture kernel config options (Arch Dependent, ppc64)
225 ----------------------------------------------------------
237 Dump-capture kernel config options (Arch Dependent, arm)
238 ----------------------------------------------------------
240 - To use a relocatable kernel,
245 Dump-capture kernel config options (Arch Dependent, arm64)
246 ----------------------------------------------------------
248 - Please note that kvm of the dump-capture kernel will not be enabled
249 on non-VHE systems even if it is configured. This is because the CPU
256 Here 'size' specifies how much memory to reserve for the dump-capture kernel
259 starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
280 on the value of System RAM -- that's mostly for distributors that pre-setup
287 range=start-[end]
291 crashkernel=512M-2G:64M,2G-:128M
297 2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
298 3) if the RAM size is larger than 2G, then reserve 128M
300 3) crashkernel=size,high and crashkernel=size,low
302 If memory above 4G is preferred, crashkernel=size,high can be used to
304 so could be above 4G if system has more than 4G RAM installed. Otherwise,
305 memory region will be allocated below 4G if available.
308 region above 4G, low memory under 4G is needed in this case. There are
309 three ways to get low memory:
311 1) Kernel will allocate at least 256M memory below 4G automatically
312 if crashkernel=Y,low is not specified.
313 2) Let user specify low memory size instead.
314 3) Specified value 0 will disable low memory allocation::
316 crashkernel=0,low
319 -----------------------
342 Load the Dump-capture Kernel
345 After booting to the system kernel, dump-capture kernel needs to be
350 of dump-capture kernel. Following is the summary.
354 - Use bzImage/vmlinuz if kernel is relocatable.
355 - Use vmlinux if kernel is not relocatable.
359 - Use vmlinux
363 - Use image or bzImage
367 - Use zImage
371 - Use vmlinux or Image
374 to load dump-capture kernel::
376 kexec -p <dump-capture-kernel-vmlinux-image> \
377 --initrd=<initrd-for-dump-capture-kernel> --args-linux \
378 --append="root=<root-dev> <arch-specific-options>"
381 to load dump-capture kernel::
383 kexec -p <dump-capture-kernel-bzImage> \
384 --initrd=<initrd-for-dump-capture-kernel> \
385 --append="root=<root-dev> <arch-specific-options>"
388 to load dump-capture kernel::
390 kexec --type zImage -p <dump-capture-kernel-bzImage> \
391 --initrd=<initrd-for-dump-capture-kernel> \
392 --dtb=<dtb-for-dump-capture-kernel> \
393 --append="root=<root-dev> <arch-specific-options>"
396 to load dump-capture kernel::
398 kexec -p <dump-capture-kernel-Image> \
399 --initrd=<initrd-for-dump-capture-kernel> \
400 --append="root=<root-dev> <arch-specific-options>"
403 loading dump-capture kernel.
425 Notes on loading the dump-capture kernel:
430 So, on non-PAE systems, ELF32 is always used.
432 The --elf32-core-headers option can be used to force the generation of ELF32
434 with ELF64 headers on 32-bit systems.
437 due to shared interrupts in the dump-capture kernel.
439 * You must specify <root-dev> in the format corresponding to the root
442 * Boot parameter "1" boots the dump-capture kernel into single-user
446 dump. Hence generally it is useful either to build a UP dump-capture
447 kernel or specify maxcpus=1 option while loading dump-capture kernel.
451 * You should enable multi-cpu support in dump-capture kernel if you intend
452 to use multi-thread programs with it, such as parallel dump feature of
453 makedumpfile. Otherwise, the multi-thread program may have a great
454 performance degradation. To enable multi-cpu support, you should bring up an
455 SMP dump-capture kernel and specify maxcpus/nr_cpus options while loading it.
474 After successfully loading the dump-capture kernel as previously
475 described, the system will reboot into the dump-capture kernel if a
477 die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).
482 will boot into the dump-capture kernel ( die_nmi() ).
486 the system will boot into the dump-capture kernel.
488 On powerpc systems when a soft-reset is generated, die() is called by all cpus
489 and the system will boot into the dump-capture kernel.
491 For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
492 "echo c > /proc/sysrq-trigger" or write a module to force the panic.
497 After the dump-capture kernel is booted, write out the dump file with
500 cp /proc/vmcore <dump-file>
502 or use scp to write out the dump file between hosts on a network, e.g::
504 scp /proc/vmcore remote_username@remote_ip:<dump-file>
507 with specified options to filter out unwanted contents, e.g::
509 makedumpfile -l --message-level 1 -d 31 /proc/vmcore <dump-file>
517 /proc/vmcore. Use the debug vmlinux built with -g and run the following
520 gdb vmlinux <dump-file>
527 ELF32-format headers using the --elf32-core-headers kernel option on the
533 https://github.com/crash-utility/crash
536 https://crash-utility.github.io/
552 This will cause a kdump to occur at the add_taint()->panic() call.
557 - [email protected]